PURPOSE: To efficiently produce a germ-free packaged food of a solid food, by decompressing the interior of a packaging container before and after thermal sterilization in packaging the food in a packaging container having an opening part closed with a sterilizing filter and thermally sterilizing the food.

CONSTITUTION: A sterilizing filter 2 having innumerable small holes capable of passing air and steam but no microorganism therethrough is bonded or fused to an opening part 1 of a packaging container so as to close the opening part 1. Solid foods, e.g. vegetable, meat, beans, etc., are contained in the packaging container and thermally sterilized. The interior of the packaging container is decompressed before the thermal sterilization treatment so as to rapidly pass heating steam through the sterilizing filter into the container. Thereby thermal sterilization is efficiently carried out. After the sterilization treatment, the interior of a sterilizing device is decompressed to smoothly carry out cooling and drying of the packaged foods.